This invention relates generally to a thin sheet orifice plate and a manufacture thereof. More specifically, this invention concerns the apparatus and method for fabricating a thin sheet orifice plate having orifices in a predetermined pattern with axes accurately conforming to predetermined directions and having rounded inlets.
The design and manufacture of thin sheet orifice plates is of importance in many spraying applications and of particular importance when the orifice plate distributes material in a plane perpendicular to direction of flow of material through the orifice plate. In the latter spraying applications, it is frequently necessary to accurately predict or determine spray coverage. Important characteristics of spray coverage are density and uniformity of material distribution and droplet size and uniformity thereof.
Density and uniformity of material distribution are characteristics related not only to the flow rate of material through the orifices but also to the direction which streams of droplets emanate from the orifices. Thus, it is apparent that flow rates and stream directions must be capable of accurate determination. The characteristics of droplet size and uniformity are also significant since they deal with the susceptibility of the spray to random cross-currents of wind, among other things.
Uniformly sized droplets, accurately predetermined directions and flow rates require that each orifice in a nozzle plate has a uniform, predetermined outlet diameter and a predetermined flow direction and volumetric flow rate. Given these characteristics desired spray coverage requirements may be attained by properly selecting the number of orifice holes and the pattern of such holes in an orifice plate.
In the past it has been known to drill orifice holes individually. However, when dealing with thin plates, for example having a thickness on the order of 0.005 inches, drilling does not provide a satisfactory technique. More specifically, it is known not only that drills frequently break and distort an orifice plate but also that the axis of a drilled hole frequently meanders thereby directing a flow of fluid out of a target area. Other problems relating to the use of drilled holes include the fact that the holes were not round and that one or more burrs were frequently left at the exit from the orifice. To even partially overcome problems of the type noted, the drilling process necessarily proceeded slowly thus adding substantially to the cost of orifice plates fabricated thereby.
Aside from the problems associated with the manufacture of orifice plates having drilled holes therethrough, additional problems arise when such orifice plates are placed into use. For example, the inability to precisely control the axis of each orifice caused unpredictable stream performance insofar as obtaining coverage in a given target area is concerned. In addition, non-uniform cross-sectional areas and sharp edged inlets led to excessive erosion of each orifice passage after short periods of use thereby destroying accuracy of flow rate estimations. Furthermore, in the presence of burrs the direction of a given stream frequently would shift erratically and generate smaller non-uniform droplets or satellites.
Another difficulty with previously known thin orifice plates concerns the propensity of small diameter orifices to clog. Such clogging is not only difficult to avoid but also adversely affects the uniformity of material distribution. Since the known thin orifice plates have been expensive to manufacture, a great reluctance to readily discard clogged orifice plates is manifested by the users.
One method of eliminating a portion of the problems related to drilled orifice holes is to use an orifice plate which is substantially thicker than the thin sheet orifice plate to be described herein. Such an approach, however, suffers from undesirably high expense for not only the plate, but also for the labor involved in manufacturing the relatively longer orifices. It is also noted that a large number of small orifices will provide a more uniform spray overage than will a small number of large orifices such as may be necessary with thicker orifice plates.
In the past, it has also been known to use punches and dies to manufacture orifice openings in orifice plates. Conventionally, however, the concept of using a punch to fabricate orifice openings in a thin sheet orifice plate blank has generally been found to be unacceptable. For example, as the punch engages the material surface, the entire sheet may be deformed and stressed until the punch penetrates the material. It should be readily apparent that such a process can lead to permanent deformations and weakened orifice plates due to excessive and repeated stresses. Such permanent deformations destroy the utility of the product by eliminating whatever control previously existed over the direction and size of the orifices.